Intense Pulsed Light (IPL) sources are used for the treatment of a variety of aesthetic skin problems, including hair removal, skin rejuvenation including wrinkle removal, treatment of vascular lesions, treatment of acne, etc. Intense pulsed light sources are broad band sources, such as Xenon flash lamps, spectrally filtered to obtain narrower and more selective emission wavelengths. Typical energy density levels utilized in hair removal are 5-50 J/cm2, with pulse durations ranging from approximately 3 to 300 msec. IPL sources are mostly operated in a multiple pulse train mode such as a 50 msec pulse which consists of three pulses of 3 msec each with a 20 msec delay between the pulses. The treatment area is often close to 1×4 cm.
Such treatment is generally conducted by trained personnel, such as nurses under the supervision of a physician. Aesthetic systems based on high intensity light are divided into monochromatic pulsed laser sources, such as described in U.S. Pat. No. 5,879,346 and non-coherent broad-band IPL sources, such as described in U.S. Pat. Nos. 5,683,380, 5,885,273, 6,187,001, 6,280,438, 6,214,034, 5,964,749, and 6,387,089.
These prior art systems are extremely risky to the eyes and may cause blindness if a bystander or a patient accidentally stares at the distal end of the treatment system. As a result, the safety level of prior art laser and IPL sources utilized for aesthetic treatments is such that protective eyeglasses are mandatory. The use of both laser and IPL sources without supervision of a physician is prohibited in many countries.
In addition to the accidental risk associated with directly staring at the distal end of a pulsed light based treatment device without wearing protective eyeglasses, there is a longer term risk associated with unavoidable staring at the treatment site. The treated skin backscatters bright light which originates from the treatment device, and the backscattered light repeatedly reaches the eyes of an operator, causing severe eye fatigue.
The conversion of an IPL aesthetic source into an inherently eye-safe device which does not require medically trained operators and which does not necessitate the use of inconvenient protective eyeglasses would therefore be advantageous. Protective eyeglasses, which are needed for the attenuation of backscattered treatment light and should transmit ambient illuminating light having a broad band spectrum for adequate visibility, limit the field of view of an operator and are opaque at a broad range of wavelengths, resulting in a darkened treatment site.
The need for protective eyeglasses during aesthetic treatments is obviated if the risks associated with direct staring at the distal end of an IPL source and with skin backscattering are eliminated. Co-pending International Patent Publication WO 03/049633 by the same applicant, the description of which is incorporated herein by reference, discloses a laser unit suitable for aesthetic treatment, which is converted into an eye-safe laser unit.
One cause of eye risk associated with aesthetic treatments with a non-coherent IPL source is the possibility of staring directly at the flash lamp through a light guide (see FIG. 2). When a light guide is not employed, as described in U.S. Pat. No. 6,187,001, direct view is even more probable. The energy density emitted directly from a flash lamp, e.g. having a size of 3×40 mm, may reach an energy density level of 40-60 J/cm2 or higher. The flash lamp may be considered a diffused light source which emits energy at a solid angle close to 3.14 steradians, achieved by ideal diffuser sources with 100% transmission and provided with Lambertian angular scattering properties. As a result, the radiance, i.e. the energy density per solid angle, of the flash lamp is close to 15-20 J/cm2/steradian. In many cases radiance may be even higher than that level. The maximal permitted radiance or accessible emission limit (AEL) emitted from an extended diffused light source used without protective eyeglasses is given in the FDA eye safety standard 1040.10 21 CFR Ch.1 and in the ANSI Z136.1 standard, and is a function of wavelength and pulse duration. If divided into narrow spectral segments, the radiance for each spectral segment is given by the equation: AEL=10*k1*k2*T^⅓, where k1 equals 1 in the visible part of the spectrum, 1.6 at a wavelength of approximately 800 nm, 3 at a wavelength of approximately 980 nm and 5 at a wavelength of approximately 1064 nm, k2=1, and T is the pulse duration expressed in seconds.
Most intense pulsed light sources operate in spectral bands having a lower limit of approximately 585 nm (k1=1) or 645 nm wavelength (k1=1) for photorejuvenation and 755 nm (k1=1.3) or 810 wavelength (k1=1.6) for hair removal. The energy content at a higher wavelength is smaller. As a result, the maximal permitted radiance from IPL sources approximates AEL=10*1.5*T^⅓. For a pulse duration of 3 msec often used for photorejuvenation, which is strongly based on absorption of light in extremely thin vessels with a thermal relaxation time of less than 1 msec, the AEL is approximately 3 J/cm2/sr, a value much less than the radiance emitted by a flash lamp of 15-20 J/cm2/sr, as referred to hereinbefore. An IPL source used with high efficacy in aesthetic treatments is therefore not eye-safe and emits a radiance which may be 6-13 times above the safe limit set by the aforementioned FDA standard. It will be appreciated that even a factor of 2 above the accepted standard for eye safety requires the use of inconvenient protective glasses during an aesthetic treatment.
It will be appreciated that there is a trade off between the efficacy of an intense light source used in aesthetic treatments and the corresponding eye or skin safety. As the efficacy is higher, the energy density is higher, and therefore there is a higher risk of burning the skin since such an intense light source is in contact with the skin. To prevent skin burning, some prior art intense light sources are provided with a chiller, which chills the skin just before firing the IPL.
Although a variety of IPL sources are used in the treatment of aesthetic skin disorders such as devices produced by LUMENIS USA (Epilight, Quantum), RADIANCY, PALOMAR (USA), DEKA (ITALY), SYNERON (Israel), and the fluorescent frequency-shifted PLASMALITE™ (USA, SWEDEN), they all suffer from the high risk associated with the existence of a direct line of sight between a flash lamp and the eye. Furthermore, prior art aesthetic systems which utilize high energy, short pulse duration flash lamps for hair removal, wrinkle removal, skin rejuvenation or the treatment of acne, lack protective measures, such as a light diffuser placed within the line of sight between the flash lamp and skin, which would obviate the use of protective eyeglasses during the treatment.
As mentioned above, in order to completely eliminate the necessity of wearing inconvenient protective eyeglasses during aesthetic treatments with IPL sources, the amount of backscattered treatment light which reaches the eyes should also be reduced.
Protective eyeglasses used in conjunction with IPL sources, such as those produced by Glendale USA, Laser-R Shield USA, Bolle, France, or Yamamoto, Japan are generally based on selective absorption of light by an optical filter. Since the protective eyeglasses used to reduce broad band radiation associated with IPL sources are dark, the visibility of the treatment site, which is usually illuminated by broad band radiation, is similarly reduced. Other protective eyeglasses, such as those disclosed in U.S. Pat. Nos. 4,462,661, 5,671,035, 5,022,742, 5,841,507, 5,519,522, 4,968,127, 5,208,688 and 6,170,947, are based on the attenuation of light by liquid crystal devices. These prior art devices are relatively heavy and cumbersome, and limit the field of view of an operator.
Additional aesthetic systems related to the current invention are devices incorporating both IPL and laser sources in a single system. For example, a “Quantum” system produced by LUMENIS incorporates a spectrally broad-band, non-coherent IPL source for hair removal or photorejuvenation and a monochromatic coherent Nd:YAG pulsed laser operated at 1064 nm for the treatment of leg veins. Coherent laser sources, like all prior art aesthetic lasers, are extremely risky to the eyes, having a radiance which is often more than 10,000 times above the AEL.
Other relevant prior art is disclosed in U.S. Pat. Nos. 5,595,568, 5,879,346, 5,226,907, 5,066,293, 5,312,395, 5,217,455, 4,976,709, 6,120,497, 5,411,502, 5,558,660, 5,655,547, 5,626,631, 5,344,418, 5,964,749, 4,736.743, 5,449,354, 5,527,308, 5,814,041, 5,595,568, 5,735,844, 5,057,104, 5,282,797, 6,011,890, 5,745,519, and 6,142,650.
If the eye safety level of a laser and of an IPL source were reduced to a level below that listed in the aforementioned standards, such a device would be able to be operated by personnel without any medical background, such as aestheticians, and also by individual users at home.
Prior art IPL sources used for aesthetic treatments are incapable of generating non-coherent light at both a high enough energy density, which would assure treatment efficacy, and at a low enough radiance, which would not present a risk of injury to the eyes of bystanders.
Subcutaneous regions commonly referred to as “hot spots,” at which the treatment energy density is much higher than the average surrounding energy density, often cause a side effect during various types of aesthetic treatments such as the treatment of vascular lesions, particularly port wine stain, or the treatment of fine wrinkles in non-ablative photorejuvenation. A noticeable side effect during the treatment of port wine stain is purpura, characterized by dark spots of severely damaged vessels which remain for a few days. A noticeable side effect caused by hot spots during the treatment of wrinkles is the coagulation of collagen zones, which may result in scarring.
With respect to laser sources, such as Dye lasers which are most commonly used for the treatment of vascular lesions (although KTP, diode and Nd:YAG lasers are also used and such side effects are also noticeable therewith), the hot spots generally result from small interference speckles. With respect to IPL sources, instabilities in the arc which generates light in the flash lamp may be responsible for the hot spots.
It would be therefore be desirable to prevent the appearance of purpura during the treatment of vascular lesions or of scarring during the non-ablative treatment of wrinkles. It would be likewise be desirable to prevent the formation of inhomogeneous hot spots under the skin surface during light-based aesthetic treatments.
Co-pending U.S. patent application Ser. No. 10/498,382 by the same applicant discloses a method and apparatus for preventing the appearance of purpura, by which a controlled vacuum is applied to a vacuum chamber in contact with a skin target, so that a significantly lower energy density level relative to prior art methods is sufficient for achieving the coagulation of blood vessels. It would be desirable to prevent the occurrence of purpura without need of having to generate a vacuum.
It is an object of the present invention to provide a non-coherent IPL source that may be used for aesthetic procedures.
It is an object of the present invention to provide a non-coherent IPL source that overcomes the disadvantages of the prior art.
It is another object of the present invention to provide an IPL source that is not injurious to the eyes of an operator or of an observer located in the vicinity of, or at a distance from, a target.
It is yet another object of the present invention to provide an IPL source which does not necessitate the use of protective eyeglasses, without causing severe eye fatigue.
It is yet another object of the present invention to provide an IPL source which could be operated by personnel without any medical background.
It is a further object of the present invention to prevent the appearance of purpura during the treatment of vascular lesions with a laser or IPL source, or of scarring during the non-ablative treatment of wrinkles.
It is a further object of the present invention to prevent the formation of multiple inhomogeneous hot spots under the skin surface during light-based aesthetic treatments.
Other objects and advantages of the invention will become apparent as the description proceeds.